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Abstract:

A method and system modify a material's characteristics. A first material
has at least one characteristic that changes in the presence of
electromagnetic energy, and a second material is positioned such that it
is in contact with the first material. The second material is
electrically conductive and sustains Surface Plasmon Polariton (SPP)
excitation and propagation when electromagnetic radiation is coupled
thereto. A diffraction grating is disposed at a planar region defined by
one of the second material and a composite of the first material and
second material. A beam of electromagnetic radiation is directed towards
the diffraction grating at an acute angle with respect to the planar
region. The electromagnetic radiation incident on the diffraction grating
is coupled to the second material whereby SPP propagation generates an
electromagnetic wave incident on at least a portion of the first material
to thereby change its characteristics.

Claims:

1. A system for modifying a material's characteristics, comprising: a
first material having at least one characteristic that changes in the
presence of electromagnetic energy; a second material in contact with
said first material, said second material being electrically conductive
and sustaining Surface Plasmon Polariton (SPP) excitation and propagation
when electromagnetic radiation is coupled thereto; a planar region
defined by one of said second material and a composite of said first
material and said second material; a diffraction grating at said planar
region; and a source for directing a beam of said electromagnetic
radiation towards said diffraction grating at an acute angle with respect
to said planar region, wherein said electromagnetic radiation incident on
said diffraction grating is coupled to said second material and wherein
said SPP propagation generates an electromagnetic wave incident on at
least a portion of said first material.

2. A system as in claim 1, wherein said second material comprises a layer
thereof on said first material.

3. A system as in claim 1, wherein said one of said second material and
said composite comprises a film.

4. A system as in claim 3, wherein thickness of said film does not exceed
approximately one micron.

5. A system as in claim 1, wherein said diffraction grating is formed at
said planar region from said one of said second material and said
composite.

6. A system as in claim 1, wherein said diffraction grating is coupled to
said one of said second material and said composite at said planar
region.

7. A system as in claim 1, wherein said first material is selected from
the group consisting of a magnetic material, a ferroelectric material,
and an optical material.

8. A system as in claim 1, further comprising a detector for detecting
intensity and polarization of a portion of said electromagnetic radiation
experiencing one of diffraction caused by said diffraction grating,
reflection from said first material, and transmission through said first
material.

9. A system as in claim 1, further comprising a third material on said
diffraction grating, said third material being adapted to react with a
material-of-interest wherein optical properties of said diffraction
grating are altered.

10. A system as in claim 9, further comprising a detector for detecting
intensity and polarization of a portion of said electromagnetic radiation
experiencing one of diffraction caused by said diffraction grating,
reflection from said first material, and transmission through said first
material.

11. A system as in claim 1, wherein said second material forms a pattern
on said first material.

12. A system as in claim 11, wherein said second material comprises a
film having a thickness that does not exceed approximately one micron.

13. A system as in claim 1, wherein said first material and said second
material are identical.

14. A system for modifying a material's characteristics, comprising: a
first material selected from the group consisting of a magnetic material,
a ferroelectric material, and an optical material, said first material
having at least one characteristic that changes in the presence of
electromagnetic energy; a second material in contact with said first
material, said second material being electrically conductive and
sustaining Surface Plasmon Polariton (SPP) excitation and propagation
when electromagnetic radiation is coupled thereto; a film defined by one
of said second material and a composite of said first material and said
second material; a diffraction grating at a surface of said film; and a
source for directing a beam of said electromagnetic radiation towards
said diffraction grating at an acute angle with respect to said surface
of said film, wherein said electromagnetic radiation incident on said
diffraction grating is coupled to said second material and wherein said
SPP propagation generates an electromagnetic wave incident on at least a
portion of said first material.

15. A system as in claim 14, wherein said second material comprises a
layer thereof on said first material.

16. A system as in claim 14, wherein thickness of said film does not
exceed approximately one micron.

17. A system as in claim 14, wherein said diffraction grating is formed
in said film.

18. A system as in claim 14, wherein said diffraction grating is coupled
to said film.

19. A system as in claim 14, wherein a portion of said electromagnetic
radiation passes through said second material and is incident on said
first material, said system further comprising a detector for detecting
intensity and polarization of said portion of said electromagnetic
radiation experiencing one of diffraction caused by said diffraction
grating, reflection from said first material, and transmission through
said first material.

20. A system as in claim 14, further comprising a third material on said
diffraction grating, said third material being adapted to react with a
material-of-interest wherein optical properties of said diffraction
grating are altered.

21. A system as in claim 20, wherein a portion of said electromagnetic
radiation passes through said second material and is incident on said
first material, said system further comprising a detector for detecting
intensity and polarization of said portion of said electromagnetic
radiation experiencing one of diffraction caused by said diffraction
grating, reflection from said first material, and transmission through
said first material.

22. A system as in claim 14, wherein said film comprises said second
material formed as a pattern on said first material.

23. A system as in claim 14, wherein said first material and said second
material are identical.

24. A method of modifying a material's characteristics, comprising the
steps of: positioning a first material in contact with a second material,
the first material having at least one characteristic that changes in the
presence of electromagnetic energy and the second material being
electrically conductive and sustaining Surface Plasmon Polariton (SPP)
excitation and propagation when electromagnetic radiation is coupled
thereto; disposing a diffraction grating at a planar region of one of the
second material and a composite of the first material and the second
material; and directing a beam of the electromagnetic radiation towards
the diffraction grating at an acute angle with respect to the planar
region, wherein the electromagnetic radiation incident on the diffraction
grating is coupled to the second material and wherein said SPP
propagation generates an electromagnetic wave incident on at least a
portion of the first material.

25. A method according to claim 24, wherein said step of positioning
comprises the step of forming the second material as a film not to exceed
approximately 1 micron in thickness on the first material.

26. A method according to claim 24, wherein said step of disposing
comprises the step of forming the diffraction grating from one of the
second material and the composite.

27. A method according to claim 24, wherein said step of disposing
comprises the step of coupling the diffraction grating to one of the
second material and the composite.

28. A method according to claim 24, wherein the first material is
selected from the group consisting of a magnetic material, a
ferroelectric material, and an optical material.

29. A method according to claim 24, further comprising the step of
detecting intensity and polarization of a portion of the electromagnetic
radiation experiencing one of diffraction caused by the diffraction
grating, reflection from the first material, and transmission through the
first material.

30. A method according to claim 24, wherein said step of positioning
comprises the step of forming the second material as a pattern on the
first material.

31. A method according to claim 24, wherein the diffraction grating
defines diffraction features, and wherein said step of directing
comprises the step of orienting the beam to be approximately
perpendicular to at least a portion of the diffraction features.

32. A method according to claim 24, further comprising the step of
depositing a third material on the diffraction grating, the third
material being adapted to react with a material-of-interest wherein
optical properties of the diffraction grating are altered.

33. A method according to claim 32, further comprising the step of
detecting intensity and polarization of a portion of the electromagnetic
radiation experiencing one of diffraction caused by the diffraction
grating, reflection from the first material, and transmission through the
first material.

34. A method according to claim 24, wherein the first material and the
second material are identical.

Description:

FIELD OF INVENTION

[0001] The field of the invention relates generally to systems and methods
for modifying physical characteristics of materials, and more
particularly to an optical method and system for modifying
characteristics of a material using Surface Plasmon Polariton (SPP)
propagation.

BACKGROUND OF THE INVENTION

[0002] Surface Plasmon Polaritons (SPPs) are transverse magnetic surface
waves propagating at the surface of an electrical conductor. SPPs result
from interactions between illuminating radiation and the free electrons
of the conductor. The propagating SPPs generate highly-confined
electromagnetic fields. Initiating and controlling SPP propagation is an
emerging field that has potential value in various electronic and optical
solid-state applications where application results typically rely on
changes in material characteristics. However, to date, simple methods and
systems that use SPP initiation/propagation to control material
properties for a broad variety of applications are not available.

BRIEF SUMMARY OF THE INVENTION

[0003] Accordingly, it is an object of the present invention to provide a
method and system for modifying a material's characteristics using SPPs.

[0004] Another object of the present invention is to provide a simple
method and system for modifying material characteristics using SPPs where
the method/system can be applied to a broad range of applications.

[0005] In accordance with the present invention, a system and method are
provided for modifying a material's characteristics. A first material has
at least one characteristic that changes in the presence of
electromagnetic energy, and a second material is positioned such that it
is in contact with the first material. The second material is
electrically conductive and sustains Surface Plasmon Polariton (SPP)
excitation and propagation when electromagnetic radiation is coupled
thereto. A planar region is defined by one of the second material and a
composite of the first material and second material. A diffraction
grating is disposed at the planar region. A source directs a beam of
electromagnetic radiation towards the diffraction grating at an acute
angle with respect to the planar region. The electromagnetic radiation
incident on the diffraction grating is coupled to the second material. As
a result, the SPP propagation generates an electromagnetic wave incident
on at least a portion of the first material to thereby change its
characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The summary above, and the following detailed description, will be
better understood in view of the drawings that depict details of
preferred embodiments.

[0007] FIG. 1 is a schematic view of a system for modifying a material's
characteristics in accordance with an embodiment of the present
invention;

[0008]FIG. 2 is a plan view of a diffraction grating schematically
illustrating the orientation of the beam of electromagnetic radiation
used to initiate the propagation of Surface Plasmon Polaritons (SPPs) in
accordance with an embodiment of the present invention;

[0009] FIG. 3 is a schematic view of a system for modifying a material's
characteristics in accordance with another embodiment of the present
invention;

[0010] FIG. 4 is a schematic view of a system that modifies the
characteristics of a magnetic data storage media for the purpose of
reading the stored data in accordance with another embodiment of the
present invention;

[0011] FIG. 5 is a schematic view of a system that modifies the
characteristics of a magnetic material for the purpose of sensing the
presence of a material-of-interest in accordance with another embodiment
of the present invention;

[0012] FIG. 6 is a schematic view of a system that modifies the
characteristics of a magnetic material in a patterned fashion for the
purpose of defining a plasmonic circuit in accordance with another
embodiment of the present invention;

[0013] FIG. 7 is a schematic view of a system that modifies the
characteristics of an optical waveguide for the purpose of changing the
optical modulation properties thereof in accordance with another
embodiment of the present invention; and

[0014]FIG. 8 is a schematic view of a system for modifying a material's
characteristics in accordance with yet another embodiment of the present
invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention is a simple method and system for modifying
the propagation of Surface Plasmon Polaritons (SPPs). As will be
explained later herein, the method and system can be used in a variety of
applications to include reading of magnetically-stored data, sensing,
plasmonic circuits, and optical modulation in waveguides. Prior to
describing these various applications, the essential principles and
elements of the method and system, respectively, will be presented.

[0016] Referring now to the drawings and more particularly to FIG. 1, an
embodiment of an optical system for modifying one or more characteristics
of a material is shown and is referenced generally by numeral 10. It is
to be understood that the shapes of the elements of system 10 and
relative sizes of the elements of system 10 (as well as other embodiments
described herein) are for purpose of illustration only and are not to
scale. System 10 includes a material 12 having one or more properties or
characteristics that are subject to change when material 12 is partially
or fully exposed to electromagnetic energy. The particular properties or
characteristics that are subject to change depend on the particular
material 12, the choice of which is dependent upon the ultimate
application of system 10. Typical properties or characteristics that
change in the presence of electromagnetic energy include magnetic
properties, ferroelectric properties, optical properties, and
magneto-optical properties. Accordingly, material 12 is typically a
magnetic, ferroelectric, or optical material.

[0017] Another material 14 is placed in contact with material 12.
Typically, material 14 is formed as a layer on a surface of material 12.
Materials 12 and 14 can be adhered or bonded to one another with the
particular bonding technique being predicated on the particular materials
12 and 14. Such bonding techniques are well known in the art and are not
limitations of the present invention. In most applications, material 14
is formed as a thin-film (i.e., on the order of approximately one micron
or less) along a planar surface of material 12 such that material 14
forms a planar, thin-film. Note that material 12 can be a thin-film or
bulk material without departing from the scope of the present invention.
For purpose of the present invention, material 14 is an electrically
conductive material and is capable of sustaining SPP excitation and
propagation when electromagnetic radiation is coupled to material 14. The
wavelength of the electromagnetic radiation is selected based on the
particular material 14 as well as the application's requirements.

[0018] A diffraction grating 16 is provided at some or all of the surface
(i.e., a planar surface) of material 14. Diffraction grating 16 can be
formed directly in material 14 or could be a separate element that is
coupled to material 14. As is known in the art, diffraction gratings are
defined by diffraction features such as parallel grooves or periodic
arrays of geometric patterns such as squares, rectangles, etc., that
cause any electromagnetic radiation incident thereon to diffract in some
known way. The particulars of diffraction grating 16 can be tailored to a
specific application of system 10.

[0019] System 10 also includes an electromagnetic (EM) radiation source 18
capable of producing a beam 20 of EM radiation having a wavelength
selected for a particular application. For example, suitable wavelengths
include those in the visible, ultraviolet, and infrared spectrums. Beam
20 is directed towards grating 16 to be incident thereon whereby
diffracted EM radiation 20A propagates to material 14. For purposes of
the present invention, the angle of incidence a that beam 20 makes with
the planar surface of material 14 is an acute angle (i.e.,
0°<α<90°). Further and as illustrated
schematically in FIG. 2, although not a strict requirement, beam 20 is
generally oriented to be perpendicular (or approximately so) to parallel
grooves (represented by dashed lines 16A) formed/defined by diffraction
grating 16. If beam 20 is not perpendicular to grooves 16A, conical
diffraction will result whereby diffraction orders of diffraction grating
16 will change and the intensity of the diffracted EM radiation will
decrease. Accordingly, changing the orientation of beam 20 relative to
parallel grooves 16A can be used as a means to adjust the results
produced by the diffracted EM radiation. If diffraction grating 16 is
realized by a periodic array of geometric patterns, beam 20 could be
oriented to be perpendicular to a particular "line" of the geometric
patterns.

[0020] The combination of material 14, diffraction grating 16, and source
18 are selected to excite and propagate SPPs along material 14 as
illustrated by wavy line 22. As a result, an electromagnetic (EM) wave 24
is generated that is incident on material 12. The energy associated with
EM wave 24 changes one or more characteristics of material 12 in some
known way to satisfy the requirements of a particular application of
system 10. The portion of material 12 subjected to the effects of EM wave
24 can be controlled by one or more of the choices of material 14,
diffraction grating 16, and source 18, as well as the location of
diffraction grating 16 as will be explained further below.

[0021] Another embodiment of the present invention is illustrated in FIG.
3 where elements common to those previously described herein utilize the
same reference numerals. In system 30, materials 12 and 14 are combined
into a composite material 32 whereby the above-described properties of
material 12 and material 14 are retained and exhibited by composite
material 32. As in the previous embodiment, composite material 32
presents a planar surface at which diffraction grating 16 is coupled to
or formed directly therein. Composite material 32 can be in the form of a
thin-film whose thickness will generally not exceed approximately one
micron. EM source 18 illuminates diffraction grating 16 with beam 20 at
acute angle α whereby the diffracted radiation 20A is coupled to
material 14. Once this occurs, SPP excitation and propagation 22 is
sustained and EM wave 24 is generated/incident on some or all of material
12 resident in composite material 32. The resultant characteristic
changes in material 12 are used by system 20 in accordance with a
particular application.

[0022] As mentioned above, the present invention can be adapted for a
variety of applications. While some exemplary applications will now be
described with the aid of FIGS. 4-7, it is to be understood that
additional applications fall within the scope of the present invention.
Each application is explained using separate (layers) for materials that
are analogous to materials 12 and 14. However, the present invention is
not so limited as applications might also be practiced using a composite
form of materials 12 and 14.

[0023] FIG. 4 illustrates a system 40 for reading stored magnetic data. In
this application, it is assumed that a magnetic material 42 (e.g.,
magnetic metals, magnetic alloys, etc.) has a number of magnetic bit
states (represented by arrows 42A) "written" therein as would be well
understood in the art of magnetic data storage. A material 44 analogous
to previously-described material 14 is provided on a planar surface of
material 42. Suitable materials for material 44 include, but are not
limited to, gold and silver. Typically, material 44 is in the form of a
thin-film (approximately one micron or less in thickness) bonded to
material 42. Diffraction grating 46 is coupled to material 44 or is
incorporated directly therein. Similar to the previous embodiments, EM
radiation source 18 directs beam 20 to be incident on diffraction grating
46 at acute angle α. The diffracted EM radiation 20A is coupled to
material 44 whereby SPPs 22 are excited/propagated such that EM wave 24
is incident on magnetic (data storage) material 42. EM wave 24 enhances
the magneto-optical activity property of magnetic material 42. That is,
exposure of magnetic material 42 to EM wave 24 increases the optical
sensitivity of magnetic states 42A. Accordingly, system 40 is configured
to confine the production of EM wave 24 to a specified region of magnetic
material 42 in order to "read" magnetic bit states 42A in the specified
region. Reading of magnetic states 42A is accomplished using an optical
detector 48 capable of detecting EM radiation 26 that reflects off
magnetic material 42 and propagates through material 44 and diffraction
grating 46. Detector 48 should be able to detect the radiation's
intensity and polarization state to determine bit state.

[0024] Referring now to FIG. 5, a system 50 is configured for sensing the
presence of a material-of-interest (e.g., a gas, particles of a
substance, biomolecules, etc.). In this application, a magnetic material
52 (e.g., magnetic metal, magnetic alloy, etc.) is used to increase the
sensitivity of system 50 to a particular material of interest. A material
54 (e.g., gold, silver, etc.) analogous to previously-described material
14 is provided on a planar surface of magnetic material 52. Once again,
material 54 will typically be a thin-film (approximately one micron or
less in thickness) bonded to material 52. Diffraction grating 56 is
coupled to material 54 or is incorporated directly therein. Deposited on
the surface of diffraction grating 56 is a reactive material 58 (e.g., a
thin-film, spray coating, etc.) selected to react (e.g., bond) with some
material-of-interest 100 that could be present in the environment where
system 50 will be used. When material-of-interest 100 is not present,
diffraction grating 56 will diffract beam 20 (from EM radiation source
18) in a known fashion. When material-of-interest 100 is present, it will
react with material 58 to thereby alter the diffraction of beam 20
incident on diffraction grating 56 based on the reaction of material 58
with material-of-interest 100. System 50 is designed such that, when
material-of-interest 100 is present, diffracted beam 20A causes changes
in SPPs 22 when EM wave 24 is incident on material 52. Magneto-optical
properties of material 52 are enhanced by SPPs and can be modulated by
application of modest (e.g., less than a few hundred oersted) external
oscillating magnetic field thereby increasing the signal-to-noise ratio
(at optical detector 48) of EM radiation 26 reflecting off material 52.
In this application, detector 48 could additionally or alternatively be
sensitive to EM radiation 28 diffracting directly from diffraction
grating 56 since its diffraction orders will be altered when
material-of-interest 100 is present. A detector (not shown) could also be
positioned to measure EM radiation 29 transmitted through material 52
where such transmission is altered when material-of-interest 100 is
present.

[0025] FIG. 6 illustrates a system 60 that is configured as a plasmonic
circuit. In this application, a magnetic, ferroelectric, or optical
material 62 has a material 64 (analogous to previously-described material
14) formed as a pattern thereon. In this embodiment, some suitable
materials 62 could be, but are not limited to, cobalt, iron and vanadium
dioxide. Suitable materials 64 include, but are not limited to, gold,
silver, and conducting transparent oxides. Material 64 is typically a
thin-film having a thickness of approximately one micron or less.
Diffraction grating 66 is coupled to or incorporated in patterned
material 64. EM radiation source 18 directs beam 20 to be incident on
diffraction grating 66 at acute angle α. Beam 20 is also typically
perpendicular to the diffraction grating's parallel grooves (represented
by straight lines 66A). Diffracted EM radiation 20A is coupled to
patterned material 64 whereby SPPs 22 and the resulting EM wave follow or
track along with patterned material 64. In this application, material 62
can also modify SPPs 22 in terms of the SPP's propagation distance and
wavelength. Accordingly, it may also be desirable to provide an external
energy source 68 (e.g., magnetic field source, thermal source, electric
field source, etc.) that can couple energy 68A to material 62 in order to
alter the magnetic properties thereof.

[0026] Referring now to FIG. 7, system 70 illustrates an optical
application of the present invention where an optical material 72 defines
a portion of a waveguide used to transmit optical energy 200. A material
74 (analogous to previously-described material 14) is in contact with
waveguide material 72. For example, material 74 could be a thin-film
(thickness of approximately one micron or less) cladding on waveguide
material 72. Diffraction grating 76 is coupled to or incorporated in
material 74. EM radiation source 18 directs beam 20 to be incident on
diffraction grating 76 at acute angle α. Diffracted radiation 20A
is coupled to material 74 whereby SPPs 22 are excited/propagated and EM
wave 24 is thereby generated. Optical properties of waveguide material 72
are modified by EM wave 24 thereby modifying the electromagnetic modes
that can be transmitted through waveguide material 72.

[0027] While the various applications of the present invention described
thus far assume the use of disparate materials (i.e., analogous to
materials 12 and 14), the present invention is not so limited. For
example, system 80 in FIG. 8 illustrates an embodiment of the present
invention using a single (thin-film) material 82 that is electrically
conductive, sustains SPP excitation/propagation when EM radiation is
coupled thereto, and possesses characteristics that are changeable in the
presence of electromagnetic energy. For example, material 82 could be
nickel, or a variety of magnetic alloys. A diffraction grating 86 can be
coupled to or incorporated in the planar surface of material 82. EM
radiation source 18 directs beam 20 to be incident on diffraction grating
86 as in the previous embodiments.

[0028] The advantages of the present invention are numerous. A simple and
efficient method of SPP excitation/propagation is used to modify the
characteristics of a material. The basic elements of the system/method
can be readily adapted to a variety of electronic and optical
applications.

INCORPORATION BY REFERENCE

[0029] All publications, patents, and patent applications cited herein are
hereby expressly incorporated by reference in their entirety and for all
purposes to the same extent as if each was so individually denoted.

EQUIVALENTS

[0030] While specific embodiments of the subject invention have been
discussed, the above specification is illustrative and not restrictive.
Many variations of the invention will become apparent to those skilled in
the art upon review of this specification. The full scope of the
invention should be determined by reference to the claims, along with
their full scope of equivalents, and the specification, along with such
variations.

Patent applications by Rosa A. Lukaszew, Williamsburg, VA US

Patent applications by COLLEGE OF WILLIAM AND MARY

Patent applications in class IRRADIATION OF OBJECTS OR MATERIAL

Patent applications in all subclasses IRRADIATION OF OBJECTS OR MATERIAL